Alignment

[[no_unique_address]] since C++20 [[no_unique_address]] applies to user-defined types (e.g., empty or stateless classes or structs). It does not apply to fundamental types (int, float, etc.), as they always require memory for storage. The attribute optimizes memory layout by allowing empty or stateless user-defined types to overlap memory locations, improving efficiency without violating the C++ object model. Motivation Prior to C++20, Empty Base Optimization (EBO) allowed an empty base class to take zero space when it was inherited by another class....

In a struct, the padded bytes depend on the alignment requirement of the next member following the current member, because the compiler must ensure proper and efficient access to memory. Alignment Requirement: Each data type has a required alignment, which is typically a power of two. For example: char: 1-byte alignment int: 4-byte alignment long (on a 64-bit system): 8-byte alignment double: 8-byte alignment Padding: When laying out struct members, if the next member needs stricter (i....

Definition of an Empty Class An empty class is a class that: Contains no non-static data members. May include: Member functions (including operator() or constructors), but these do not contribute to the class size. Static data members, because these are shared across all instances and are not part of the object layout. Does not use virtual functions or polymorphism, which would require the inclusion of a vtable pointer. Inherits from another empty class, as the derived class can still remain empty due to Empty Base Optimization (EBO)....